Go into the root directory where Interstate 82 has been installed. You will find a file called "User" - This is the file which contains all the information about what vehicle and weapons you currently have.
In the root directory you will also have a sub directory called "Variant" - This is where all the information about other vehicles (Including news vehicles created for the "Instant Action" missions) are stored.
You can view all these files with Notepad, as they are text files. (You can view the names of the variants to find the correct vehicle you want.)
All that needs to be done, is to delete the "User" file, and copy one of the "Variant" files into the root directory, and rename it to "User".
If you then ALT - TAB back into the game, and select "Customize Car", you should have your new vehicle in place of your old one.
(Note - The last vehicle you used in the previous mission, is automatically selected when you rejoin a saved game. For this reason, you cannot edit the "User" file before you start Interstate '82 as it will be overwritten.)
LOVE Kill All Enemies on Radar (SP Only)
CUDDLE Car is Invulnerable (SP Only)
HUGS Make Friendlies Invulnerable (SP Only)
CARESS Full Ammo
IMLAME Auto-win Mission
SYRUP AI Vehicles Stop, but can still shoot (SP Only)
MRFREEZE Freeze Time for all AI
NUKEME Suicide
zz_autobahn.cfg = Makes foreign cars selectable in multiplayer
zz_airlift.cfg = Modifies the Load Mission window so that you can load any mission. Requires an existing saved game to exist.
zz_creditline.cfg = No cash limit in the trip missions. You can buy anything that is currently available.